§ 221. Company stores. No person engaged in construction of public work under contract with the state or with any municipal corporation either as a contractor or subcontractor shall, directly or indirectly, conduct what is commonly known as a company store if there is any store selling supplies within two miles of the place where such contract is being executed. Charges for groceries, provisions, board, lodging or clothing shall not be a valid off-set in behalf of the employer against wages.